1. Field of the Invention
This invention has as its object an active matrix display screen with row and column redundancy.
It finds an applicatin in optoelectronics in the production of liquid crystal displays used particlarly as converters of electrical data into optical data.
2. Discussion of the Background
An active matrix display screen generally comprises two plates between which is inserted an electrooptical material such as a liquid crystal. On one of the plates is a matrix of transparent conductive blocks, thin-film transistors, a family of conductive addressing rows and a family of conductive addressing columns. Each transistor has a gate connected to a row, a source connected to a block and a drain connected to a column. On the second plate is a counterelectrode.
Such a structure is shown in FIG. 1. Represented there in a simplified manner is a lower plate 10 carrying conductive coluns 12 and conductive rows 14, a transistor 20 and a conductive block 22 and an upper plate 24 covered with a counterelectrode 26.
In FIG. 2 is shown the equivalent diagram of the overall display screen an element of which has been described in figure 1. This screen comprises conductive columns 12, connected to a control circuit 28 delivering suitable video voltages, and conductive rows 14, connected to a control circuit 30 delivering line addressing voltages. In dashed lines, picture points 32 of the display screenhave beenshown. they are located at the intersection of rows 14 and conductive columns 12. These picture points 32 (also called "pixels") each comprise a transistor 20 and a capacitor. One of the capacitor plates consists of a conductive block 22 deposited on plate 10 and the other capacitor plate consists of a counterelectrode 26 deposited on the other plate 24.
With reference to this figure, it is seen that in case a conductive line (either a column 12, or a row 14) is broken, the broken line portion is no longer brought to the control potetial delivered by control circuit 28 or 30.
This results in the nonfunctioning of the pixels connected to this line portion, which is reflected by a very visible spurious effect on the display screen. This effect can, for example, be a white streak corresponding to the defective pixels connected to the broken line portion on a black screen background.